It is often desired to quantitatively assess the intensities of the color of red lines on a white test strip. For example, US Patent Publication 2004/0131238 describes a method of assessing the color intensity of colored lines on white test strips by analyzing one or more individual scan lines taken in the direction of the long dimension of the test strip, so, if it is desired to use the data from multiple scan lines, either the long dimension of the sample must have been oriented perfectly in parallel to the direction of the scan, or else the data analysis needs to be extremely complicated. It is desired to provide a method of analyzing the intensities of the colors of red lines on a white test strip that involves relatively simple calculations and that is not affected by variations in the angle between the long axis of the test strip and the direction of the scan.